1. Technical Field
The following description relates generally to a microwave signal generator. More particularly, the following description relates to a microwave signal generator capable of filtering for a microwave signal corresponding to an intrinsic oscillation frequency of a magnetron from microwave signals generated by the magnetron and using the microwave signal to control the oscillation frequency of the magnetron.
2. Background
Typically, a microwave signal generator uses a traveling wave tube (TWT) or a magnetron to generate a microwave signal. The TWT is very expensive, and thus most microwave signal generators use an inexpensive magnetron to generate a microwave signal.
In one conventional magnetron, a pure copper electrode is arranged as an anode, and a cathode and a grid are axially arranged. With a magnetic field applied in a direction axial of the cathode, electrons radially sputter from the cathode and move toward the anode, which simultaneously receive a force from the magnetic field in a direction perpendicular to a progressing direction of the electrons. As a result, the electrons may perform a spiral movement.
If strength of the magnetic field is increased, the path of the electrons is bent even more causing the electrons to repeatedly rotate before reaching the anode. If the strength of the magnetic field reaches a critical field value (threshold flux density), the chances are that electrons will continuously rotate and not reach the anode at all.
At this time, a rotating electron cloud is generated about the cathode, and an induction current is generated at a vibration circuit of the anode to allow resonance to continue. The oscillation frequency of the magnetron is primarily determined by the vibration circuit. In this manner, the magnetron is capable of producing highly efficient and highly powered electromagnetic energy.
A microwave signal generator for generating a microwave signal using the magnetron is commonly employed in a microwave oven. Such a microwave signal generator could be also used in a PLS (Plasma Lighting System).
The PLS may be configured such that a microwave signal generated by a microwave signal generator is transmitted to a cylindrical oscillator via a waveguide. The oscillator is disposed with an electrode-less bulb having light emitting material hermetically sealed therein. The microwave signal transmitted to the oscillator excites the light emitting material into plasma, which emits visible light or ultraviolet ray.
The PLS typically has a long life and superior illumination over an incandescent light or a fluorescent light widely used for lighting systems, such that the PLS may serve as a light source in a variety of applications such as street lightings. Furthermore, the PLS may be used in large spaced area as opposed to relatively cramped and closed spaced area.
An oscillation frequency of the magnetron may vary unpredictably in response to a load change and an output change of the magnetron itself. The microwave signal generator for generating microwave signals using the magnetron may also generate side bands and harmonics in addition to the main microwave signals of intrinsic high frequency band.
For reasons as described above, the oscillation frequency of the magnetron may not be fixed to one frequency, but may generate several oscillation frequencies due to its intrinsic characteristics and influence by external loads to thereby cause interference with communication within a region.
For instance, there may be a high likelihood that frequency bands of microwave signals generated by the microwave signal generator create interference with frequency bands used for Wibro communication, HSDPA (High Speed Downlink Packet Access), wireless LAN (Local Area Network. IEEE 802.22 standards), Zigbee (IEEE802.15 standards), Bluetooth (IEEE802.15 standards), RFID (Radio Frequency Identification) and satellite telephones.